Mark,
There is too much here and I wish to address each point in order not to loose in the intended post and expand on your thoughts if I may.
I'm not sure if "the" lab is needed, or if it's simply that the top end nic handlers all perform a reasonable analysis of the nic content, whether done in-house or through an outside group (and I wouldn't care if it was from one specific lab or any lab with the right tools).
Absolutely true dependent on the size of the operation. It might prove to be cost effective to have a chemist and equipment on hand when some vendors are dealing in large volumes (think totally wicked) who orders 100,000 units of whatever at any given time. <--- not necessarily nic related. That being said, proper prtocol is in place, have been endorsed by ECITA and welcome random testing at any time.
Using TPA for GC/MS (I hadn't known TPA did this until I saw the BE report, but, yes, it's listed under their available services

) is not bad, nor is having it done by someone else. If the focus is on just checking for the nic concentration, is GC/MS even a requirement, or would a titration performed by a professional be reasonable?
GC/MS is the way to go. After all we have seen and discussed in the last week, titration only provides a ball park figure. The former although more expensive validates slightly more expensive liquids (a portion of the cost past down to the consumer (for small operations)) This point has already been voiced by the community. For large operations such as TW, the large portion of this cost merely goes into overhead as a business expense. When dealing with the volume of liquid generated, not all associated cost should be the responsibility of the vendor and it is totally acceptable IMO that a certain (small) portion be levied against the customer.
If someone ran a high-end test earlier, super, but I would absolutely expect that each bottle coming out the door can directly trace to a test result showing that the bottle has the labeled value.
With this portion you are dreaming. never going to happen nor should we expect it to be the norm neither. This would entail that every bottle leaving the premises be tested. However, If 5 gals of liquid X was tested to be Y from drum Z, it is safe to assume because of the check and balances of a reputable company that bottle XYZ conforms to its label.
Any volume vendor would hopefully be working off of larger source containers, for example a 5 gallon mix of 60 mg/ml, which is used to create bottles of 60mg/ml for sale. The 5 gallon final mix container is where the lot # should come into play for outside use, the larger container of 60mg/ml from which bottles for sale are produced, tied to a single final test result. The label on the bottle should clearly have a lot # indicated, and it should be possible to look up the tested value.
Answered above.
(There is a customer training aspect to this, people will need to learn that the 100mg/ml label may really test as 102, or 98, and still be within reasonable manufacturing tolerances -- surprise!)
Not the vendors responsibility. All they are required to do if provide traceability from cradle to grave. What you chose to do with your bottle is entirely up to you, and does not fall under their realm of liability nor responsibility, because accurate documentation from their and random testing outweigh any test you might have conducted at the kitchen table.
Issues of cleanliness, material handling, etc. are separable.
While a vendor group checking to see that vendors are indeed doing the tests that they record, and is able to do an audit of a sample, is good, I personally wouldn't expect or require such things to occur all that frequently. The sealed bottles, chain of custody, sending things to a central authority to then pass along for formal tests is a bit more onerous or administration heavy than I would expect to be needed for normal operations, the kind of thing I would expect if a vendor has seemed to lapse than how ongoing activities would occur. My starting point is the idea that vendors are generally good people trying to do the right thing, but a bit of framework providing best practices would help.
Exactly! Once vendor has established that he has always been in compliance, then the focus of the governing body needs to shift to more problematic areas if any. That is the purpose of a properly functioning regulator. Having said that, this does not go to say they never get tested again - just the periodicity extended.
(I absolutely agree with Jan that if a second tier vendor then does anything, in any way, to the incoming nic from the first vendor, other than strictly rebottling, then there should be a new lot number, with backup test, showing that the output is what it is said to be. The simplest example would be if a lower tier vendor buys quantity 100mg/ml, then does their own internal cutting to create a 50 mg/ml for resale -- that 50 should be checked, and have its own new lot number.)
It is incumbent of any receiver that receives nicotine to perform testing upon receipt of said product and compare test results against COA. That being said, if the liquid is to be sold unadjusted, not re-identification is required of said bottles. OTOH should the liquid be further reduced, then by all means a new identifier should be used for traceability purposes e.g company A received 5 gals of liquid B. 3 Gals were sold as is, and the remainder of the 2 gals were sold as 50, 48, and 36mg. Then yes a new identifier is required should a"a particualr concentration" become problematic, it is easily identified and a recall only needs to be done lets say on 36mg.